The present invention generally relates to combustion initiation of fuel-air mixtures. More particularly, the invention concerns an apparatus and method for combustion of fuel-air mixtures in internal combustion engines employing a coil-on-plug ignition system.
The purpose of an ignition system is to initiate combustion of a flammable fuel-air mixture by igniting the mixture at precisely the right moment. In spark-ignition engines, this is achieved with an electrical spark. Specifically, an electrical ark is formed between a center electrode and a ground electrode of a spark plug. A voltage, or electrical potential difference builds between the spark plug electrodes until a spark arks from the center electrode to the ground electrode. An ignition wire, or spark plug cable delivers the electrical energy from a coil to a spark plug boot that attaches the spark plug cable to the spark plug.
Efforts to improve the durability and reliability of ignition systems have focused on eliminating the spark plug cable. Removing spark plug cables also allows the removal of heat shields and cable looms, with the attendant elimination of voltage leaks and engine misfires caused by faulty spark plug cables. However, with the elimination of spark plug cables, individual coils must be placed near each spark plug, hence the xe2x80x9ccoil-on-plugxe2x80x9d or xe2x80x9ccoil-near-plugxe2x80x9d ignition system. A typical coil-on-plug ignition system includes a coil mounted on top of, or adjacent to each spark plug. A spark plug boot carries the electrical current from the coil to the spark plug. Where the coil is mounted adjacent to the spark plug, a short cable is used to connect the coil to the spark plug boot. In contrast to single-coil systems, with one coil supplying electrical energy to all of the engine""s spark plugs, a coil-on-plug system uses a single coil to supply the electrical energy to a single spark plug. This allows the elimination of spark plug cables and their problems, but coil-on-plug ignition systems have their own problems.
Each ignition coil must be compact enough to meet engine-bay packaging requirements, while also avoiding interference with other engine components. These small coils can have difficulty generating the energy necessary to produce a spark that can reliably combust the fuel-air mixture. Moreover, to keep costs at a minimum, these small coils are designed to generate only just enough electrical energy to initiate combustion in a new, perfectly tuned engine. As carbon deposits build up in the combustion chamber, and engine timing deteriorates, reliable combustion also declines.
Moreover, initiating combustion in modern-day spark ignition engines is becoming increasingly difficult. This is because new fuel-efficient engine designs use lean fuel-air mixtures that are difficult to ignite. Turbochargers and superchargers are also used to increase engine efficiency, but the increased combustion chamber pressures they generate further suppress combustion. In addition, the gap between the electrodes in the spark plugs continues to increase, which increases the amount of electrical energy necessary to create a spark.
The present invention alleviates to a great extent the disadvantages of conventional coil-on-plug ignition systems by providing a capacitor that stores electrical energy received from the coil and delivers it to the spark plug to produce a powerful spark, thereby increasing combustion efficiency and decreasing harmful environmental emissions.
In a preferred embodiment, a capacitor is formed by a center element, an insulator and a cylinder head. A spark plug boot includes the center element that is structured to carry electric current from a coil to the spark plug located at the bottom of a cylinder head cavity. An insulator surrounds the center element, with an outer surface of the insulator sized to engage a surface of the cylinder head cavity. The spark plug boot is configured so that the center element, insulator and cylinder head comprise a capacitor that stores an electrical energy received from the coil, and discharges it to form a powerful spark at the spark plug.
One aspect of the invention includes a method for optimizing a storage capacity of the capacitor formed by the spark plug boot and the cylinder head. The method comprises the steps of determining an available electric energy from a coil-on-plug ignition system communicating with the capacitor, selecting an optimum capacitance value for the ignition system by finding a maximum capacitance value and subtracting a safety margin, and adjusting a capacitance of the capacitor to approximate the optimum capacitance value. The maximum capacitance value is determined when the spark plug only sparks sporadically and the safety margin is determined when the spark plug sparks consistently.
In another aspect of the present invention, the spark plug boot comprises a center element structured to carry electric current from the coil to the spark plug, with the spark plug comprising a first electrical path to ground. An insulator surrounds the center element, with an outer surface of the insulator sized to engage the cylinder head. The center element, insulator and cylinder head comprise a capacitor, with the capacitor having a second electrical path to ground, so that the spark plug and the capacitor are electrically connected in parallel. This increases the efficiency of the capacitor thereby increasing the electrical energy delivered to the spark plug.
Another embodiment of the present invention optimizes spark duration by including a resistor in the spark plug boot. The resistor and capacitor formed by the spark plug boot and cylinder head are sized to deliver an optimum spark by determining an available electrical energy from the capacitor, and selecting an ideal resistance value based on the available energy, wherein the ideal resistance value creates an optimum duration spark, thereby maximizing combustion of the fuel-air mixture.
These and other features and advantages of the present invention will be appreciated from review of the following detailed description of the invention, along with the accompanying figures in which like reference numerals refer to like parts throughout.